[crossgen2] Promote single byref aot. (#65682)

* Rename `CORINFO_FLG_DONT_PROMOTE` to `CORINFO_FLG_DONT_DIG_FIELDS`.

* Support promotion of `struct{ 1 gcref; }` outside of version bubble.

src/coreclr/inc/corinfo.h

@@ -841,7 +841,7 @@ enum CorInfoFlag
     CORINFO_FLG_ARRAY                 = 0x00080000, // class is an array class (initialized differently)
     CORINFO_FLG_OVERLAPPING_FIELDS    = 0x00100000, // struct or class has fields that overlap (aka union)
     CORINFO_FLG_INTERFACE             = 0x00200000, // it is an interface
-    CORINFO_FLG_DONT_PROMOTE          = 0x00400000, // don't try to promote fields (used for types outside of AOT compilation version bubble)
+    CORINFO_FLG_DONT_DIG_FIELDS       = 0x00400000, // don't ask field info, AOT can't rely on it (used for types outside of AOT compilation version bubble)
     CORINFO_FLG_CUSTOMLAYOUT          = 0x00800000, // does this struct have custom layout?
     CORINFO_FLG_CONTAINS_GC_PTR       = 0x01000000, // does the class contain a gc ptr ?
     CORINFO_FLG_DELEGATE              = 0x02000000, // is this a subclass of delegate or multicast delegate ?

src/coreclr/jit/compiler.h

@@ -4149,6 +4149,8 @@ class Compiler
         void PromoteStructVar(unsigned lclNum);
         void SortStructFields();
 
+        bool CanConstructAndPromoteField(lvaStructPromotionInfo* structPromotionInfo);
+
         lvaStructFieldInfo GetFieldInfo(CORINFO_FIELD_HANDLE fieldHnd, BYTE ordinal);
         bool TryPromoteStructField(lvaStructFieldInfo& outerFieldInfo);
 

src/coreclr/jit/compiler.hpp

@@ -4480,9 +4480,9 @@ inline static bool StructHasCustomLayout(DWORD attribs)
     return ((attribs & CORINFO_FLG_CUSTOMLAYOUT) != 0);
 }
 
-inline static bool StructHasNoPromotionFlagSet(DWORD attribs)
+inline static bool StructHasDontDigFieldsFlagSet(DWORD attribs)
 {
-    return ((attribs & CORINFO_FLG_DONT_PROMOTE) != 0);
+    return ((attribs & CORINFO_FLG_DONT_DIG_FIELDS) != 0);
 }
 
 //------------------------------------------------------------------------------

src/coreclr/jit/lclvars.cpp

@@ -1685,13 +1685,6 @@ bool Compiler::StructPromotionHelper::CanPromoteStructType(CORINFO_CLASS_HANDLE
     structPromotionInfo.fieldCnt = (unsigned char)fieldCnt;
     DWORD typeFlags              = compHandle->getClassAttribs(typeHnd);
 
-    if (StructHasNoPromotionFlagSet(typeFlags))
-    {
-        // In AOT ReadyToRun compilation, don't try to promote fields of types
-        // outside of the current version bubble.
-        return false;
-    }
-
     bool overlappingFields = StructHasOverlappingFields(typeFlags);
     if (overlappingFields)
     {
@@ -1709,6 +1702,26 @@ bool Compiler::StructPromotionHelper::CanPromoteStructType(CORINFO_CLASS_HANDLE
     unsigned structAlignment = roundUp(compHandle->getClassAlignmentRequirement(typeHnd), TARGET_POINTER_SIZE);
 #endif // TARGET_ARM
 
+    // If we have "Custom Layout" then we might have an explicit Size attribute
+    // Managed C++ uses this for its structs, such C++ types will not contain GC pointers.
+    //
+    // The current VM implementation also incorrectly sets the CORINFO_FLG_CUSTOMLAYOUT
+    // whenever a managed value class contains any GC pointers.
+    // (See the comment for VMFLAG_NOT_TIGHTLY_PACKED in class.h)
+    //
+    // It is important to struct promote managed value classes that have GC pointers
+    // So we compute the correct value for "CustomLayout" here
+    //
+    if (StructHasCustomLayout(typeFlags) && ((typeFlags & CORINFO_FLG_CONTAINS_GC_PTR) == 0))
+    {
+        structPromotionInfo.customLayout = true;
+    }
+
+    if (StructHasDontDigFieldsFlagSet(typeFlags))
+    {
+        return CanConstructAndPromoteField(&structPromotionInfo);
+    }
+
     unsigned fieldsSize = 0;
 
     for (BYTE ordinal = 0; ordinal < fieldCnt; ++ordinal)
@@ -1760,21 +1773,6 @@ bool Compiler::StructPromotionHelper::CanPromoteStructType(CORINFO_CLASS_HANDLE
     noway_assert((containsGCpointers == false) ||
                  ((typeFlags & (CORINFO_FLG_CONTAINS_GC_PTR | CORINFO_FLG_BYREF_LIKE)) != 0));
 
-    // If we have "Custom Layout" then we might have an explicit Size attribute
-    // Managed C++ uses this for its structs, such C++ types will not contain GC pointers.
-    //
-    // The current VM implementation also incorrectly sets the CORINFO_FLG_CUSTOMLAYOUT
-    // whenever a managed value class contains any GC pointers.
-    // (See the comment for VMFLAG_NOT_TIGHTLY_PACKED in class.h)
-    //
-    // It is important to struct promote managed value classes that have GC pointers
-    // So we compute the correct value for "CustomLayout" here
-    //
-    if (StructHasCustomLayout(typeFlags) && ((typeFlags & CORINFO_FLG_CONTAINS_GC_PTR) == 0))
-    {
-        structPromotionInfo.customLayout = true;
-    }
-
     // Check if this promoted struct contains any holes.
     assert(!overlappingFields);
     if (fieldsSize != structSize)
@@ -1790,6 +1788,62 @@ bool Compiler::StructPromotionHelper::CanPromoteStructType(CORINFO_CLASS_HANDLE
     return true;
 }
 
+//--------------------------------------------------------------------------------------------
+// CanConstructAndPromoteField - checks if we can construct field types without asking about them directly.
+//
+// Arguments:
+//   structPromotionInfo - struct promotion candidate information.
+//
+// Return value:
+//   true if we can figure out the fields from available knowledge.
+//
+// Notes:
+//   This is needed for AOT R2R compilation when we can't cross compilation bubble borders
+//   so we should not ask about fields that are not directly referenced. If we do VM will have
+//   to emit a type check for this field type but it does not have enough information about it.
+//   As a workaround for perfomance critical corner case: struct with 1 gcref, we try to construct
+//   the field information from indirect observations.
+//
+bool Compiler::StructPromotionHelper::CanConstructAndPromoteField(lvaStructPromotionInfo* structPromotionInfo)
+{
+    const CORINFO_CLASS_HANDLE typeHnd    = structPromotionInfo->typeHnd;
+    const COMP_HANDLE          compHandle = compiler->info.compCompHnd;
+    const DWORD                typeFlags  = compHandle->getClassAttribs(typeHnd);
+    if (structPromotionInfo->fieldCnt != 1)
+    {
+        // Can't find out values for several fields.
+        return false;
+    }
+    if ((typeFlags & CORINFO_FLG_CONTAINS_GC_PTR) == 0)
+    {
+        // Can't find out type of a non-gc field.
+        return false;
+    }
+
+    const unsigned structSize = compHandle->getClassSize(typeHnd);
+    if (structSize != TARGET_POINTER_SIZE)
+    {
+        return false;
+    }
+
+    assert(!structPromotionInfo->containsHoles);
+    assert(!structPromotionInfo->customLayout);
+    lvaStructFieldInfo& fldInfo = structPromotionInfo->fields[0];
+
+    fldInfo.fldHnd = compHandle->getFieldInClass(typeHnd, 0);
+
+    // We should not read it anymore.
+    fldInfo.fldTypeHnd = 0;
+
+    fldInfo.fldOffset  = 0;
+    fldInfo.fldOrdinal = 0;
+    fldInfo.fldSize    = TARGET_POINTER_SIZE;
+    fldInfo.fldType    = TYP_BYREF;
+
+    structPromotionInfo->canPromote = true;
+    return true;
+}
+
 //--------------------------------------------------------------------------------------------
 // CanPromoteStructVar - checks if the struct can be promoted.
 //
@@ -2761,7 +2815,7 @@ void Compiler::makeExtraStructQueries(CORINFO_CLASS_HANDLE structHandle, int lev
     assert(structHandle != NO_CLASS_HANDLE);
     (void)typGetObjLayout(structHandle);
     DWORD typeFlags = info.compCompHnd->getClassAttribs(structHandle);
-    if (StructHasNoPromotionFlagSet(typeFlags))
+    if (StructHasDontDigFieldsFlagSet(typeFlags))
     {
         // In AOT ReadyToRun compilation, don't query fields of types
         // outside of the current version bubble.

src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs

@@ -2028,7 +2028,7 @@ private uint getClassAttribsInternal(TypeDesc type)
             if (!_compilation.CompilationModuleGroup.VersionsWithType(type))
             {
                 // Prevent the JIT from drilling into types outside of the current versioning bubble
-                result |= CorInfoFlag.CORINFO_FLG_DONT_PROMOTE;
+                result |= CorInfoFlag.CORINFO_FLG_DONT_DIG_FIELDS;
                 result &= ~CorInfoFlag.CORINFO_FLG_BEFOREFIELDINIT;
             }
 #endif

src/coreclr/tools/Common/JitInterface/CorInfoTypes.cs

@@ -594,7 +594,7 @@ public enum CorInfoFlag : uint
         CORINFO_FLG_ARRAY = 0x00080000, // class is an array class (initialized differently)
         CORINFO_FLG_OVERLAPPING_FIELDS = 0x00100000, // struct or class has fields that overlap (aka union)
         CORINFO_FLG_INTERFACE = 0x00200000, // it is an interface
-        CORINFO_FLG_DONT_PROMOTE = 0x00400000, // don't try to promote fieds of types outside of AOT compilation version bubble
+        CORINFO_FLG_DONT_DIG_FIELDS = 0x00400000, // don't try to ask about fields outside of AOT compilation version bubble
         CORINFO_FLG_CUSTOMLAYOUT = 0x00800000, // does this struct have custom layout?
         CORINFO_FLG_CONTAINS_GC_PTR = 0x01000000, // does the class contain a gc ptr ?
         CORINFO_FLG_DELEGATE = 0x02000000, // is this a subclass of delegate or multicast delegate ?